The advent of combination antiretroviral therapy, including protease inhibitors, has greatly reduced the rates of AIDS-related mortality and morbidity in the United States. However, recent studies reveal high rates of treatment failure over time and development of drug resistance, which are often associated with insufficient adherence. Poor adherence not only has personal health consequences, but also public health consequences as shown by recently documented cases of multidrug-resistant viral transmission. Despite years of research, there is still no "gold standard" adherence measure. In earlier studies, patient diaries were commonly used for assessment, but more recently electronic monitoring has been considered by many to be the preferred method. While both methods have been used widely in other medical research, little has been published to date in HIV-related studies. Diaries are sometimes considered interventions as well as assessments, while electronic monitoring has not been regarded in this manner; however, neither assumption has been directly studied. The proposed study is designed to determine whether patient diaries and electronic monitoring are simply assessment tools for estimating medication adherence, or whether they alter the behavior being assessed and thus also constitute interventions. Patients on combination antiretroviral therapy will be randomly assigned to an adherence surveillance method (microelectronic caps or patient diaries) or a no-surveillance control group. At baseline and after one month, each participant will be administered a detailed structured interview of medication adherence, which has been used successfully in ACTG and other trials. If electronic monitoring does not alter behavior, its validity as a "gold standard" adherence measure will be enhanced. Similarly, if diaries do not change adherence then they provide an inexpensive and accessible measure for both clinical and research applications. If these methods do alter medication taking behavior, such information will be useful in estimating true effect size in future research as well as translation of protocol findings to "real world" clinical settings.